ZX81 image problems

Discussions about Sinclair ZX80 and ZX81 Hardware
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1024MAK
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Re: ZX81 image problems

Post by 1024MAK »

This video on YouTube shows someone loading 1K chess link. As you can see from the video, the LCD TV can’t make sense of the output of the ZX81 during loading, so acts as if there is no signal. The picture returns once the ZX81 has finished loading.

Note that longer programs take a lot longer than this 1K byte version of chess!

Mark
paulwilco
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Re: ZX81 image problems

Post by paulwilco »

1024MAK wrote: Mon Jan 03, 2022 7:53 pm Ahh, now that you have attached the photo, it’s easy for us to see the problem. The inverse S means syntax error. While the machine detects a syntax error, it will refuse the command or program line.

Code: Select all

LOAD “”
is a shortened version of the command.
LOAD requires a string expression. A simple literal string in a program or command has to be enclosed in double quotes.
So the following are all valid:

Code: Select all

LOAD “GAME”

LOAD “PROGRAM”

LET A$=“GAME”
LOAD A$
If a string expression is given, the machine will look for a tape file/program with that exact name, then load it.
It will not load a program that has a different name.

However, if the string expression has no characters, the machine will load the first tape file/program that it detects. In other words, the name does not matter.

And because of this, and because it’s quicker to enter,

Code: Select all

LOAD “”
and is now the most common usage.

The double double quote symbol on the Q key has a special usage, so it’s not valid for use in place of two separate double quote characters.

Note that LOAD on it’s own is also not valid.

Mark
Thanks very much for this explanation Mark, makes sense now!
1024MAK wrote: Mon Jan 03, 2022 8:55 pm This video on YouTube shows someone loading 1K chess link. As you can see from the video, the LCD TV can’t make sense of the output of the ZX81 during loading, so acts as if there is no signal. The picture returns once the ZX81 has finished loading.

Note that longer programs take a lot longer than this 1K byte version of chess!

Mark
That's similar to what it's doing except it goes straight to no signal and never comes back. Does the audio in suffer with issues at all? The tzxduino is definitely outputting an audio signal.
desiv
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Re: ZX81 image problems

Post by desiv »

Just have to ask, are you plugging the audio cable into the EAR plug on the ZX81?
And are you using a MONO or a stereo cable with your TZXDuino (did it come with a cable?)?
I've been using a MONO cable with both my PC and my home-built TZXDuino (v1.18).

Also, I'd try with a very short program at first. It can take longer than you think (at least longer than I think) to load a program.

Good luck!
paulwilco
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Re: ZX81 image problems

Post by paulwilco »

I'm plugging it into the mic port. Although in desperation I've tried both! I am, however, using a stereo cable. I've ordered a mono one, hopefully this will do the trick.
desiv
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Re: ZX81 image problems

Post by desiv »

It's the EAR port...

Try that.
Also, I have used the Java program tapeutils.jar to play .P files to my TS1000. Volume was I think about 79% on my PC...
It's here:
http://www.zx81stuff.org.uk/zx81/tapeut ... rview.html
It's not the most intuitive program tho. You have to load the .P file, click OK on the info screen that pops up, then go to one of the menus and choose play...
Good luck, it might require the mono cable tho...

I tried some stereo cables on my PC and didn't have much luck with those...
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1024MAK
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Re: ZX81 image problems

Post by 1024MAK »

Just to be totally clear. The Ear and Mic sockets on a ZX81 are mono. They are not compatible with stereo 3.5mm plugs (see the photo in this post). Are you using a mono plug?

Is the output of your TZXDuino a mono or a stereo socket?

If it’s mono, you need to use a mono plug. If it’s stereo, you need to use a stereo plug.

For going from a stereo plug to mono, only use one channel (normally it’s recommended to use the left channel).

Remember, the sockets on a ZX81 are named the same as those on a shoe box cassette tape recorder, the intention being that a cable connects the ZX81 Mic socket to the cassette tape recorder mic input socket. And a cable connects the cassette tape recorder ear socket to the ZX81 ear socket.

Hence the ZX81 outputs on the mic socket, and expects inputs on it’s ear socket. It is different to the ZX Spectrum. In a ZX81 there is no internal connection between the two.
desiv wrote: Mon Jan 03, 2022 10:18 pm Also, I'd try with a very short program at first. It can take longer than you think (at least longer than I think) to load a program.
I second that!

Mark
paulwilco
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Re: ZX81 image problems

Post by paulwilco »

I think the output of the tzxduino is mono. I think that may be the problem. That and getting the wrong connector! Ill should be receiving the mono cable in a few days so ill let you know the result.

The naming of the connectors makes sense now you've explained it!
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1024MAK
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Re: ZX81 image problems

Post by 1024MAK »

paulwilco wrote: Tue Jan 04, 2022 4:25 pm I think the output of the tzxduino is mono. I think that may be the problem. That and getting the wrong connector! Ill should be receiving the mono cable in a few days so ill let you know the result.
Yes, I would expect the TZXDuino to be mono. But not having one, and there being a number of variations, I was unsure if they normally have a mono 3.5mm output socket, or use a 3.5mm stereo socket.

Mark
paulwilco
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Re: ZX81 image problems

Post by paulwilco »

Hi everyone,

Just a quick update, I received the mono cable today and it works.

At last I was able to load a game on the zx81!

Thanks again for all your help

Paul
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1024MAK
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Re: ZX81 image problems

Post by 1024MAK »

Happy days 8-)

Mark
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